The serial printer has its printing head moved at a right angle with respect to the paper feeding direction.
FIG. 9 shows a structure of the printer of this kind according to the prior art. As shown, a carrier 61 carrying a printing head 60 is supported to move at a right angle with respect to the paper feeding direction (i.e., normal to the surface of the sheet of FIG. 9) by means of a pair of guide pins 63 and 64 which extend in parallel with a platen 62. For the printing operation, the printer is so charged with an ink ribbon cassette 65 that an ink ribbon 66 may be threaded between the nose portion 60a of the printing head 60 and the platen 62.
With this structure, however, the printing head 60 cannot be adjusted back and forth with respect to the platen 62, thus causing inconvenience. For example, the clearance between the nose portion 60a of the printing head 60 and the platen 62 is so small (e.g., usually 0.2 to 0.3 mm) that the ink ribbon 66 is hard to thread through the clearance when the printer is charged with the ink ribbon cassette 65. When the printer is to be set with (not shown) sheets of recording paper, they are inconveniently hard to thread between the nose portion 60a of the printing head 60 and the platen 62.
In a conventional printing head reciprocation mechanism of a serial type dot printer, a carriage is slidably supported by a pair of parallel guide rods and a printing head is securely mounted on a carriage. The carriage is moved along the pair of parallel guide rods by a timing belt or the like so that the printing head is reciprocably moved.
As a result, a large carriage which is slidably fitted on a pair of guide rods is needed so that there arises the problem that a printing head guide device becomes large in size.